Formation Damage Issues Impacting the Productivity of Low Permeability, Low Initial Water Saturation Gas Producing Formations

Abstract

Very low in situ permeability gas reservoirs (Kgas<0.1mD) are very common and represent a major portion of the current exploitation market for unconventional gas production. Many of these reservoirs exist regionally in Canada and the United States and also on a worldwide basis. A considerable fraction of these formations appear to exist in a state of noncapillary equilibrium (abnormally low initial water saturation given the pore geometry and capillary pressure characteristics of the rock). These reservoirs have many unique challenges associated with the drilling and completion practices required in order to obtain economic production rates. Formation damage mechanisms affecting these very low permeability gas reservoirs, with a particular emphasis on relative permeability and capillary pressure effects (phase trapping) will be discussed in this article. Examples of reservoirs prone to these types of problems will be reviewed, and techniques which can be used to minimize the impact of formation damage on the productivity of tight gas reservoirs of this type will be presented.

Laboratory tests for the application of nitrate-based inhibitor against H₂S formation

“…Good results were also obtained at the concentration of the inhibitor amounting to 1000-1400 ppm; in this case the level of H 2 S decreased from the initial value of 35.8 mg/dm 3 to the value within the range of 25.0-28.7 mg/dm 3 after 24 hours of incubation. After 48 hours of incubation, the level of hydrogen sulfide decreased to the range of 24.1-25.8 mg/dm 3 . It corresponds to ca.…”

“…3), the content of neutralized hydrogen sulfide in the solution was low and amounted to ca. 0.9-6.6 mg/dm 3 . It shows that efficient content of the tested inhibitor in laboratory conditions concerns the concentrations exceeding 1000 ppm.…”

“…The results of the efficiency of BMF Bac 4 preparation at the concentrations of 1000-1400 ppm, after 24 hours and 48 hours of incubation showed the decrease in the content of hydrogen sulfide by ca. 21.0-27.5 mg/dm 3 . This test demonstrated a slight decrease in the content of hydrogen sulfide in test samples at the concentrations of the inhibitor from 100 to 500 ppm.…”

“…A third type is developed from extraneous water introduced into the formation at the wellbore causing liquid blocking during drilling, coring, completion or workover. A fourth type is due to caving and subsequent flow of unconsolidated sands into the wellbore [1,3,5,22].…”

“…Natural gas deposits as well as gas accompanying crude oil often contain an important amount of hydrogen sulfide (Barnówko-Mostno-Buszewo oil field may constitute an example as the content of this substance was reaching 40 g/Nm 3 ). In order to protect the atmospheric air, the system of constant hydrogen sulfide detection is used in this type of deposits.…”